1. Field of the Invention
The present invention relates to seats for wheel-tractors, construction machinery and the like, powered military vehicles of all kinds, and more generally to any vehicle intended for travelling on uneven grounds or off the road and wherein the absence of a suspension system or the inefficiency of the existing suspension system does not provide a sufficient degree of comfort for the driver and/or the user.
2. Description of the Prior Art
Various types of seats intended for vehicles of the abovementioned types and equipped with suspension systems providing an elastic return action and the damping of the seat oscillation in case of shocks and jolts in a vertical plane, are already known in the art. In a known construction, the seat is connected to a frame structure through linkage means constituting a parallel motion mechanism in which the lower links are rigidly coupled to a rubber ring capable of providing said elastic return action and damping the oscillation. This rubber ring in shear- and torsion stressed, and adapted to damp out both shocks and oscillation due to the inherent rubber hysteresis.
Another known construction comprises two pairs of pivoted arms disposed laterally between the squab-supporting cradle and the seat base, the ends of said arms being adapted to move along horizontal runways or guide-paths provided on said cradle and said base. The four arms or links are identical and form two "X", the upper arms being longer than the lower arms. The suspension member of this seat consists of a transverse torsion bar having one end adjustably anchored and the other end adapted to co-act with a link.
Experience teaches that these arrangements are not capable of fully damping out all shocks and oscillation, notably when the second construction is used, which is relatively complicated and expensive to manufacture. Moreover, in this second device, the reaction force of the torsion bar constituting the elastic member is transmitted to only one side of the mechanism, thus causing twistings in, and consequently abnormal kinkings of, the various metal components of the suspension system. As a result, more pronounced wear and tear of the pivot means are observed on one side of the seat as compared with the opposite side.
U.S. Pat. No. 3,752,432 discloses a seat provided with a hydropneumatic damping device. However, this device has no monitor which would permit automatic adjustment of the seat height in actual service as a function of the driver's or occupant's weight.
U.S. Pat. No. 3,879,007 describes a vehicle seat provided with a damper consisting of a cylinder and piston unit. Thus, this seat has the disadvantages mentioned above, such as, excessive height, tendency to abnormal wear, change of damping characteristics with time, and so forth.
With the hydraulic control circuit described in this U.S. Pat. No. 3,879,007 the driver, before utilizing the seat, must manually adjust its height as a function of his own weight. More particularly, he sets a three-way valve manually to a position "R" to raise the seat, and actuating the same valve to another position "L" will lower it.
Having thus adjusted the seat level, the driver shuts the valve and the seat oscillations are damped only by an accumulator and control valves.
It is clear that this system is also ill suited for adapting the seat to automatic monitoring adjustment.
U.S. Pat. No. 3,300,203 describes a seat provided with a cylinder supporting the seat frame structure and connected to a hydropneumatic damping device. This device shares the disadvantages of The device taught in U.S. Pat. No. 3,879,007. Again, no automatic monitoring device is incorporated in this seat suspension system.
In the vehicle seat disclosed in French Patent Application Ser. No. 76.21065 these inconveniences are partially avoided by providing a suspension system comprising a central inclined main beam pivotally connected between the base frame and the rear portion of an upper frame which supports the seat squab, the main beam co-acting with a pair of parallel lateral arms pivotally connected between the rear portion of the base frame and the front portion of the seat squab frame. Each lateral arm is rigidly connected intermediate its ends to a transverse shaft which itself is trunnioned in said main beam.
Here, the rigid main beam transmits the reaction torque to an elastic member and this elastic member tends to counteract the vertical movements of the seat squab frame. The assembly of the pivoted beam and pivoted arms pivoted according to the above-described arrangement constitutes a rigid system in which the seat squab frame can move uniformly vertically with suspension vibration.
Additionally, a set of rollers associated with the main beam and the lateral arms is adapted to keep the seat in a plane slightly inclined to the horizontal when the seat squab frame is shaken vertically.
This arrangement is particularly advantageous but cannot completely eliminate parasitic mechanical friction between the elements of the system.